Wind tunnel droplet dispenser



April 30, 1963 W. K. KERN WIND TUNNEL DROPLET DISPENSER Filed June 27,1961 2 Sheets-Sheet 1 April 30, 1963 w. K. KERN 3,087,332

WIND TUNNEL DROPLET DISPENSER Filed June 27, 1961 2 Sheets-Sheet 2INVENTOR. Mam 5e 4 k5? United States Patent Ofitice 3,087,332 PatentedApr. 30., 1963 3,037,332 WIND TUNNEL DROPLET DISPENSER Werner K. Kern,Tallahassee, Fla., assignor to the United States of America asrepresented by the Secretary of the Air Force Filed June 27, 1961, Ser.No. 120,097 4 Claims. (Cl. 73-147) (Granted under Title 35, US. Code(1952), sec. 266) The invention described herein may be manufactured andused by or for the United States Government for governmental purposeswithout payment to me of any royalty thereon.

This invention relates to wind tunnels, and more particularly to a noveldroplet dispenser adapted to provide a liquid spray of controllablequality and quantity therein.

Wind tunnels, such as are used in testing aircraft, are commonlyprovided with means for simulating actual flying conditions. These meansinclude temperature controls, apparatus for varying wind velocity, andliquid dispensing equipment.

In order to realistically correlate wind tunnel data to actualenvironmental data, a need exists for effective droplet dispenser meanscapable of filling wind tunnel chambers with controlled amounts ofliquid particulates of known droplet size without heating thedispensedliquid significantly above ambient temperature.

Accordingly, it is a principal object of my invention to provide new andimproved apparatus for dispensing liquid in a wind tunnel.

It is another primary object of my invention to provide a wind tunneldroplet dispenser adapted to accurately control the quantity and qualityof the liquid being dispensed therein.

Still another object of my invention is to provide a wind tunnel liquiddispensing apparatus comprising a plurality of vibrating members incombination with a controllable piezo-electric transducer.

Yet another object of my invention is to provide apparatus adapted toatomize any liquid into minute individual particles of predeterminedsize.

The above-mentioned and other features and objects of the invention, andthe manner of obtaining them will be come more apparent by reference tothe following description taken in conjunction with the accompanyingdrawings, wherein:

FIGURE 1 is a perspective view of apparatus embodying my invention;

FIGURE 2 illustrates, diagrammatically, the fluid input end of onevibrating member of the FIGURE 1 apparatus; and

FIGURE 3 is a perspective view of a Wind tunnel lending itself topractice of my invention.

In essence, my invention comprises a plurality of liquid dispensingmembers arranged in a parallel relationship within a wind tunnel, theupper ends thereof protruding through the top surface of the wind tunnelenvelope in such a manner as to receive metered amounts of liquid, andthe lower ends protruding through the bottom surface of said envelopeand in contact with pieZo-electric crystal vibrating means. I havediscovered that a liquid residing on the outer surface of a vibratingmember such as the liquid dispensing members comprehended by myinvention will collect at points of high amplitude and be. dispensed inthe form of a jet or spray. Furthermore, the droplet size, or quality ofdispensed liquid, has been found to be capable of direct correlation tothe frequency of vibration. My invention therefore utilizes this conceptby providing a variable frequency piezo-electric transducer, a pluralityof liquid dispensing members, and controllable liquid input means in anovel combination adapted to develop a spray of known quantity andquality.

Referring now to FIGURE 1, there is illustrated one presently preferredembodiment of my invention in conjunction with typical wind tunnel 5.The liquid to be dispensed by the present invention is stored incontainer 6, said container being positioned abovethe wind tunnel toenable gravity feed through spigot 30. Spigot 30 provides for controlledamounts of liquid to be dispensed through dispensing pan 7. Troughs 8are arranged below dispensing pan 7 and are supplied with equal amountsof liquid through spigots 27, 28 and 29. Troughs 8 have a plurality ofapertures in the bottoms thereof adapted to supply equal amounts offluid to each of the several liquid dispensing members. The liquiddispensing members comprehended by my invention consist of hollowtubular members having input sections 16, constricted areas It} andelongated tubular sections 9. Constricted areas 10 are situated withinthe wind tunnel and are streamlined to minimize turbulence within thetunnel. Input portions 16 are adapted to receive the liquid from troughs8 in such a manner that it will ultimately flow over the outer surfaceof constricted area 10. Said input section 16 is illustrated in detailin FIGURE 2, and will be more fully described in conjunction therewith.The several liquid dispensing members are arranged in vertical parallelrelationship through the center portion of the wind tunnel asillustrated. Elongated sections 9 of said liquid dispensing members arearranged to protrude through the lower surface of the wind tunnel andare immersed in viscous liquid 13. Container 11 which is located beneathsaid wind tunnel is provided with cooling coils 12 through which acoolant such as water may be pumped. Piezo-electric crystal 14 is placedwithin said container 11 and is in direct contact with bottom portions26 of the. several liquid dispensing members, and provides therethroughdi1 rect coupling of mechanical vibrations therefrom. Electrical inputto piezo-electric crystal 14 is made at points 24 and 25 whereby aninput signal is provided therethrough from oscillator 21 and frequencycontrol means 22.

Referring now to FIGURE 2, there is illustrated in detail the dropletdispenser input section. This comprises liquid receptacle 19, saidreceptacle having a plurality of perforations 18 on the bottom surfacethereof. Stopper 20 is inserted in the necvk of constricted portion 10thereby prohibiting the liquid from collecting within the dropletdispenser. The liquid therefore passes from trough 8 to container 19 andis spread over the outer surface of constricted portion 10 throughperforations 18.

In accordance with the principles of my invention, an oscillating signalapplied to piezo-electric crystal 14 will cause said crystal to vibratemechanically which, in turn, causes an extremely vigorous vibration inconstricted sections 10 of said liquid dispensing members. The inducedvibrations spread the dispensing liquid over these constriction surfacesand throw off said liquid in the form of small jets of spray. I havediscovered that the spray emitted from the constriction is not due toultrasonic heat ing effects, but is due to cavitation activity at theinterface. The liquid, therefore, collects at points of high amplitudewithin the constriction and it is at these points that the droplets areformed and ejected. Constricted areas 10 are also designed such thattheir nodal points, When in resonance, are at points that meet with thetunnel Walls. This provides for airtight non-gasket junctions allowingfor easy insertion and maintenance. In applications where a small amountof liquid leakage is permissible, the restriction may be designed toextend through the wind tunnel walls, as illustrated in FIGURE 1. Sincethe ultra sonic vibrations are physically small, openings in the tunnelwall need not be extremely large. For example, a liquid dispensingmember whose section 9 has a diameter of 2.5 cm. and whose constriction10 is 7 mm. will produce droplets of 4 to-5 microns when subjected toultra sonic vibrations from a piezo-electric crystal operating at afrequency of 2.4 megacycles per second.

There has thus been described novel apparatus whereby the severalobjects of my invention are achieved. While I have described above theprinciples of my invention in connection with specific apparatus, it isto be clearly understood that this description is made by way of exampleonly and not as a limitation to the scope of my invention ing saidmembers, and wherein said liquid dispensing members have constrictedportions formed in an airfoil configuration, said constricted portionsbeing physically arranged within said wind tunnel such that minimum air'flow turbulence is achieved.

2. In a wind tunnel, apparatus for providing a liquid spray comprising aplurality of liquid dispensing members arranged in vertical parallelrelationship within said wind tunnel, said members consisting ofelongated tubular elements having a constricted diameter over asubstantial portion thereof, means for coating the outer surface of saidmembers with liquid, means for controllably vibrating said members, andwherein said means for coating the outer surface of said dispensingmembers with liquid comprises a controlled fluid input source incombination with fiuid receptacle means, said receptacle meanscomprising a cup formed on the top of each said dispensing member havinga plurality of perforations therein adjacent to the outer surface of theconstricted portions of said dispensing members.

3. In a wind tunnel, apparatus for providing a liquid spray comprising aplurality of liquid dispensing members arranged in vertical parallelrelationship within said Wind tunnel, said members consisting ofelongated tubular elements having a constricted diameter over asubstantial portion thereof, means for coating the outer surface of saidmembers with liquid, means for controllably vibrating said members, andwherein said means for controllably vibrating said members comprises apiezoelectric transducer element in combination with oscillator meansand frequency control means, said transducer element being in directcontact with the bottom extremity of said dispensing members.

4. In a wind tunnel, a liquid droplet dispenser comprising a pluralityof cylindrical dispensing elements, each of said elements having as anintegral part thereof an aerodynamically contoured portion ofsubstantially smaller cross sectional area protruding longitudinallytherefrom, said elements being arranged to position said aerodynamicallycontoured portion in vertical relationship within said wind tunnel withsaid cylindrical portions protruding through the lower surface thereof,means for distributing controlled amounts of liquid over the outersurface of said aerodynamically contoured portions, and means forinducing longitudinal vibrations in said dispensing elements.

References Cited in the file of this patent UNITED STATES PATENTS2,515,069 Zola July 11, 1950 2,740,202 Fowle Apr. 3, 1956 2,744,410Browning May 8, 1956 2,968,584 Dickey Jan. 17, 1961 s ins! a 72,,

1. IN A WIND TUNNEL, APPARATUS FOR PROVIDING A LIQUID SPRAY COMPRISING APLURALITY OF LIQUID DISPENSING MEMBERS ARRANGED IN VERTICAL PARALLELRELATIONSHIP WITHIN SAID WIND TUNNEL, SAID MEMBERS CONSISTING OFELONGATED TUBULAR ELEMENTS HAVING A CONSTRICTED DIAMETER OVER ASUBSTANTIAL PORTION THEREOF, MEANS FOR COATING THE OUTER SURFACE OF SAIDMEMBERS WITH LIQUID, MEANS FOR CONTROLLABLY VIBRATING SAID MEMBERS, ANDWHEREIN SAID LIQUID DISPENSING MEMBERS HAVE CONSTRICTED PORTIONS FORMEDIN AN AIRFOIL CONFIGURATION, SAID CONSTRICTED PORTIONS BEING PHYSICALLYARRANGED WITHIN SAID WIND TUNNEL SUCH THAT MINIMUM AIR FLOW TURBULENCEIS ACHIEVED.